The effect of BDNF val66met polymorphism on visuomotor adaptation.

Brain-derived neurotrophic factor (BDNF) plays an important role in learning, memory, and brain plasticity. Humans with a val66met polymorphism in the BDNF gene have reduced levels of BDNF and alterations in motor learning and short-term cortical plasticity. In the current study, we sought to further explore the role of BDNF in motor learning by testing human subjects on a visuomotor adaptation task. In experiment 1, 21 subjects with the polymorphism (val/met) and 21 matched controls (val/val) were tested during learning, short-term retention (45 min), long-term retention (24 h), and de-adaptation of a 60° visuomotor deviation. We measured both mean error as well as rate of adaptation during each session. There was no difference in mean error between groups; however, val/met subjects had a reduced rate of adaptation during learning as well as during long-term retention, but not short-term retention or de-adaptation. In experiment 2, 12 val/met and 12 val/val subjects were tested on a larger 80° deviation, revealing a more pronounced difference in mean error during adaptation than the 60° deviation. These results suggest that BDNF may play an important role in visuomotor adaptive processes in the human.

The trampoline aftereffect: the motor and sensory modulations associated with jumping on an elastic surface.

After repeated jumps over an elastic surface (e.g. a trampoline), subjects usually report a strange sensation when they jump again overground (e.g. they feel unable to jump because their body feels heavy). However, the motor and sensory effects of exposure to an elastic surface are unknown. In the present study, we examined the motor and perceptual effects of repeated jumps over two different surfaces (stiff and elastic), measuring how this affected maximal countermovement vertical jump (CMJ). Fourteen subjects participated in two counterbalanced sessions, 1 week apart. Each experimental session consisted of a series of maximal CMJs over a force plate before and after 1 min of light jumping on an elastic or stiff surface. We measured actual motor performance (height jump and leg stiffness during CMJ) and how that related to perceptual experience (jump height estimation and subjective sensation). After repeated jumps on an elastic surface, the first CMJ showed a significant increase in leg stiffness (P < or = 0.01), decrease in jump height (P < or = 0.01) increase in perceptual misestimation (P < or = 0.05) and abnormal subjective sensation (P < or = 0.001). These changes were not observed after repeated jumps on a rigid surface. In a complementary experiment, continuous surface transitions show that the effects persist across cycles, and the effects over the leg stiffness and subjective experience are minimized (P < or = 0.05). We propose that these aftereffects could be the consequence of an erroneous internal model resulting from the high vertical forces produced by the elastic surface.

Movement observation specifies motor programs activated by the action observed objective.

There are human cortical areas that fire both when a person executes an action and when he observes someone performing a similar action. The observer activates a motor program that resembles the observed action. However, it is not known whether the motor program activated via action observation is muscle specific. In this study, using simple pulse transcranial magnetic stimulation (TMS) applied over the primary motor cortex (M1), we investigated whether the Mirror System activates a muscle specific motor program, or codes the observed action in terms of its goal. The results showed that when subjects observed a static effector in front of an object, cortical excitability was enhanced even in muscles not involved in the observed movement, but that are able to achieve the goal of the action. When there was an effector-object interaction the motor program activated via action observation is muscle specific. These results suggest that when subjects observe an object related action there is an activation of a motor program based on the observed action goal, that is transformed into a muscle specific program when the subject shows an effector-object interaction.

Ventral premotor to primary motor cortical interactions during noxious and naturalistic action observation.

Within the motor system, cortical areas such as the primary motor cortex (M1) and the ventral premotor cortex (PMv), are thought to be activated during the observation of actions performed by others. However, it is not known how the connections between these areas become active during action observation or whether these connections are modulated by the volitional component induced by the action observed. In this study, using a paired pulse transcranial magnetic stimulation (ppTMS) method, we evaluated the excitability of PMv-M1 connections during the observation of videos showing a human hand reaching to grasp a ball (naturalistic grasping video) or a switched on soldering iron (noxious grasping video). The results show that the observation of the naturalistic grasping action increased the M1 excitability and changed the strength of the PMv-M1 connections. The observation of the noxious grasping action did not induce any change in the excitability of the PMv-M1 connections throughout the video, but the strength of PMv-M1 connectivity was reduced. These results demonstrate that the PMv-M1 connections are modulated differently depending on whether the action observed would or would not be performed in real life.